1. Field of the Invention
The present invention relates to a method of and apparatus for forming closures for reclosable pouches, and more particularly, to an extrusion process and apparatus for forming multiple closure elements.
2. Description of the Background of the Invention
A reclosable thermoplastic pouch includes a closure disposed at a mouth of the bag. Recently, pouches have been developed wherein the closure comprises multiple closure elements. The closure is typically formed by extruding two closure elements connected by an intermediate portion through an aperture of a die plate. An example of one such closure, depicted in FIG. 1, includes adjacent closure elements 11 connected by a base portion 13. Another example of such a closure, depicted in FIG. 2, includes two closure elements integrally extruded with a bag web such that the closure elements are connected by an intermediate bag web portion. It can be difficult to design a die plate for extruding such closures because of difficulties encountered in controlling neck-in and shrinkage of the extruded elements.
Zieke et al. U.S. Pat. No. 4,741,789 discloses a zipper and a method of extruding the zipper onto a plastic film web. The zipper includes a base member, a single closure member protruding from the base member, and a pair of guide ribs on the base member on opposite sides of the closure member. During formation of the zipper, the web is drawn from a roll over a lamination cylinder, and the base member is extruded onto the web as the web passes over the lamination cylinder. The single closure member and ribs are then extruded onto the base member as the film and base member pass over the lamination cylinder. The single closure member and the two guide ribs are extruded through separate apertures that are vertically spaced from and laterally overlapping each other.
Goulde U.S. Pat. No. 4,835,835 discloses a method of extruding a fastener strip having a plurality of interlocking closure elements. The interlocking elements are connected by a base portion. The closure elements and the base portion are extruded through a single die plate aperture.
DiPietro et al. U.S. Pat. No. 5,411,692 discloses a method of and apparatus for extruding a bag film and a closure profile integrally connected to the bag film. A single die is used for extruding the film and closure profile. The film is extruded through a main plenum and the closure profile is extruded through a channel that is diverted from the main plenum. The channel and the main plenum converge upstream of a die exit port so that the closure profile is reunited with the film prior to exiting the die.
Tomic et al. U.S. Pat. No. 5,425,911 discloses a method of extruding a bag film with an integral closure strip having two interlocking closure elements and a die assembly for use in the method. The film is extruded through a thin outlet port between two opposing die lips in the die assembly. The closure elements are extruded integrally with the film through a set of grooves in one of the die lips.
Plourde U.S. Pat. No. 6,080,252 discloses a method of forming a zipper component for subsequent attachment to a bag wall. A flange is extruded onto a continuous carrier web, and a single profile is extruded onto the flange while the flange is on the carrier web. The resulting component is then cooled and stripped from the carrier web.